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ovl: handle idmapped mounts in ovl_set_acl()

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The two checks ovl_set_acl() performs on the overlay inode itself -
inode_owner_or_capable() and the setgid-stripping test - were done with
&nop_mnt_idmap.  On an idmapped overlay mount this compares the overlay
inode's id space directly against the caller's: it denies the rightful
owner (as seen through the mount idmap) the right to set an ACL, and
evaluates the setgid-drop decision in the wrong id space, which can
mis-set the mode on the upper inode.

Use the struct mnt_idmap passed in by the VFS for both.  Fold the
open-coded "caller not in group and not CAP_FSETID privileged" test
into in_group_or_capable() with i_gid_into_vfsgid(), the same
idmap-aware helpers used by setattr_should_drop_sgid().

The subsequent internal forced setgid-kill via ovl_setattr() stays on
&nop_mnt_idmap: it carries only ATTR_KILL_SGID with no uid/gid to
translate and is overlayfs' own mode change, not a user-driven
operation through the mount.

No functional change until FS_ALLOW_IDMAP is set on ovl_fs_type.

Link: https://patch.msgid.link/20260615-work-idmapped-overlayfs-v1-5-7381632aa402@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2026-06-15 15:19:54 +02:00
parent 22b27d403d
commit d1f78a3fed
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 3 additions and 3 deletions
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6
fs/overlayfs/inode.c
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@ -550,7 +550,7 @@ int ovl_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
return -EOPNOTSUPP;
if (type == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode))
return acl ? -EACCES : 0;
if (!inode_owner_or_capable(&nop_mnt_idmap, inode))
if (!inode_owner_or_capable(idmap, inode))
return -EPERM;
/*
@ -558,8 +558,8 @@ int ovl_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
* be done with mounter's capabilities and so that won't do it for us).
*/
if (unlikely(inode->i_mode & S_ISGID) && type == ACL_TYPE_ACCESS &&
!in_group_p(inode->i_gid) &&
!capable_wrt_inode_uidgid(&nop_mnt_idmap, inode, CAP_FSETID)) {
!in_group_or_capable(idmap, inode,
i_gid_into_vfsgid(idmap, inode))) {
struct iattr iattr = { .ia_valid = ATTR_KILL_SGID };
err = ovl_setattr(&nop_mnt_idmap, dentry, &iattr);